Determination of unit cell

The ability to obtain diffraction patterns with a large angular view has significantly enhanced the ease and potential of electron diffraction studies in the determination of unit cells and identification of submicron phases. Convergent beam electron diffraction (CBED) provides a two-dimensional projection of the three-dimensional reciprocal lattice and can be utilized to reconstruct the unit cell dimensions. In particular, the spacing of the reciprocal lattice layers parallel to the electron beam and the location and distribution of the reflections in the first and higher order Laue zones with respect to the zero layer provide information which cannot be obtained from the zero layer pattern alone. This additional information permits the identification of crystal structures of phases under investigation with previously established ones or the determination of a new structure, if previously unknown. The article describes the principles of the analysis and illustrates the application of the methods with examples from commercial material systems.